<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGL paint</title>
</head>
<style>
    canvas {
        width: 512px;
        height: 512px;
    }
</style>
<body>
    <canvas ></canvas>
    <script>
        // 创建绘制上下文
        const canvas = document.querySelector('canvas')
        const gl = canvas.getContext('webgl')

        // 创建 WebGL 程序
        const vertex = `
            attribute vec2 position;
            varying vec3 color;

            void main() {
                gl_PointSize = 1.0;
                color = vec3(0.5 + position * 0.5, 0.0);
                gl_Position = vec4(position * 0.5, 1.0, 1.0);
            }
        `

        const fragment = `
            precision mediump float;
            varying vec3 color;

            void main() {
                gl_FragColor = vec4(color, 1.0);
            }
        `

        const vertexShader = gl.createShader(gl.VERTEX_SHADER)
        gl.shaderSource(vertexShader, vertex)
        gl.compileShader(vertexShader)

        const fragmentShader = gl.createShader(gl.FRAGMENT_SHADER)
        gl.shaderSource(fragmentShader, fragment)
        gl.compileShader(fragmentShader)

        const program = gl.createProgram()
        gl.attachShader(program, vertexShader)
        gl.attachShader(program, fragmentShader)
        gl.linkProgram(program)
        gl.useProgram(program)

        // 将数据放入缓存区

        // 定义三角形顶点
        const points = new Float32Array([-1, -1, 0, 1, 1, -1])

        // 将定义好的数据写入 WebGL 的缓冲区
        const bufferId = gl.createBuffer()
        gl.bindBuffer(gl.ARRAY_BUFFER, bufferId)
        gl.bufferData(gl.ARRAY_BUFFER, points, gl.STATIC_DRAW)

        // 将缓冲区数据读取到 GPU
        const vPosition = gl.getAttribLocation(program, 'position')
        gl.vertexAttribPointer(vPosition, 2, gl.FLOAT, false, 0, 0)
        gl.enableVertexAttribArray(vPosition)

        // 执行着色器程序完成绘制
        gl.clear(gl.COLOR_BUFFER_BIT)
        gl.drawArrays(gl.TRIANGLES, 0, points.length / 2)

    </script>
</body>
</html>